Question

A scientist has a house just beside a busy highway. He collects leaves from some plants growing in his garden to do radio-carbon dating (to estimate the age of the plant by estimating the amount of a radioisotope of carbon in its tissues). Surprisingly the radio-carbon dating shows that the plant is a few thousand years old.

(a) Was the result of the radio-carbon dating wrong or can you propose a reason for such an observation?

(b) What simple experiment can be done to test the reason that you have proposed?

Answer 1

(a) The result of radio-carbon dating was correct.

Reason Vehicles running on the highway beside the house emitted carbon dioxide from the combustion of petrol or diesel, which are fossil fuels. The carbon in this carbon dioxide, coming from living material that has been converted into petroleum millions of years ago, would get assimilated into the tissues of the plant as it uses carbon dioxide from the surrounding atmosphere for photosynthesis. Therefore, tissues of the plant, when used for radio-carbon dating, would show the age of the plant to be many thousands of years old.

(b) A simple experiment to test the validity of this explanation would be to collect seeds from the plants and grow them in a plot of land away from the highway or other sources of CO₂ coming from the burning of fossil fuels.

Radio-carbon dating of plants growing from these seeds should show them as young plants.